Laser levels are used in surveying and building construction. Such laser levels project a laser beam perpendicular to a vertical axis and rotate the laser beam around the axis. The plane of the laser beam is horizontal and can therefore be used as a reference elevation.
In building large conical structures, such as the floors of concentrators and digesters it is often important that the conical surface be symmetrical and have a uniform slope. This can be done with a laser level, by varying the height of the laser level and marking the desired elevations in concentric circles. There are many steps in laying out a conical surface with this method. Each step introduces a potential for errors.
Willetts, U.S. Pat. No. 5,142,788 discloses a laser compass which may be used for laying out large circles on surfaces, such as ceilings. The Willetts device includes a laser and a rotating mirror. The laser generates a laser beam which is projected along an axis onto the rotating mirror and is deflected by the rotating mirror. As the mirror rotates the deflected laser beam is swept around a cone-shaped surface. The accuracy of the device described in U.S. Pat. No. 5,142,788 may be impaired if the bearings on which the rotating mirror is mounted are not perfect. The device is therefore difficult to adopt for use in accurately aligning large conical surfaces where high precision is required without using prohibitively expensive bearings.